I trying to use a new sensor the KMX63 with a Arduino Uno board, my sensor is on a evaluation board made by kionix.For the connexion il linked as follows:

| Pin Uno | Pin evaluation board |
| A5 | 5 |
| A4 | 7 |
| 3.3 | 1 |
| GND | 8 |

Here the schematic of the evaluation board:

I found a technical note from the constructor that advice to do some steps after the power up of the sensor to insure it's well functioning I wrote a code following it:

#include <Wire.h>#include "KMX62.h"void setup(){  Serial.begin(9600);  Wire.begin();  Serial.println(F("Starting"));  byte error=7;  byte id=0;  byte command=0;  delay(60);  Wire.beginTransmission(KMX62_I2C_ADD_2);  Wire.write(0x7F);  Serial.println(F("Write 0x7F"));  Wire.write(0x00);  Serial.println(F("Write 0x00"));  delay(100);  error=Wire.endTransmission();  Serial.print(F("retour 1 : "));  Serial.println(error);  if( error==0 ){    Wire.beginTransmission(KMX62_I2C_ADD_2);    Wire.write(CNTL2);    Wire.write(0x00);    error=Wire.endTransmission();    if( error==0 ){      Wire.beginTransmission(KMX62_I2C_ADD_2);      Wire.write(CNTL1);      Wire.write(0x80);      error=Wire.endTransmission();      if(error==0){        delay(5);        Wire.beginTransmission(KMX62_I2C_ADD_2);        Wire.write(WHO_AM_I);        Wire.endTransmission(false);        Wire.requestFrom(KMX62_I2C_ADD_2,1);        id=Wire.read();        error=Wire.endTransmission();        if(id==0x18||id==0x2D){          Wire.beginTransmission(KMX62_I2C_ADD_2);          Wire.write(COTR);          Wire.endTransmission(false);          Wire.requestFrom(KMX62_I2C_ADD_2,1);          command=Wire.read();          error=Wire.endTransmission();          if(command==0x55){            Serial.println(F("device ok"));          }else{            Serial.println(F("Issue with the sensor step e : need to be rebooted"));          }        }else{          Serial.println(F("Issue with the sensor step d id=wrong : need to be rebooted"));        }      }else{        if(error==2||error==3){        Serial.println(F("Issue with the sensor step c : need to be rebooted"));        }      }    }else{      if(error==2||error==3){        Serial.println(F("Issue with the sensor step b : need to be rebooted"));      }    }  }}void loop(){}

but i have an issue the steps , the program seem to freeze when i try to write into the register 0x7F.
I don't get any trace that i should have after the wire.endtransmission().
Here the trace i obtain :

09:56:35.477 -> Starting09:56:35.511 -> Write 0x7F09:56:35.511 -> Write 0x00

i have use the I2C scanner to check if the sensor appear, i had to modify the scanner to add a delay before Wire.beginTransmission and the Wire.endTransmission to avoid the scanner to be freeze too at the first address tried. After the modification i did saw the sensor at the address it was mean to be.here the trace for the I2C scanner :

Scanning...I2C device found at address 0x0F  !done

Anyone have an idea of why i can't write anything to my sensor without making my program freeze indefinitely each time ?

PS : After the advice of chrisl i rerunned all my programs on a arduino mini pro on 3.3V / 8Mhz and got the same result.

• 1
  Can you explain the "delay(100)" before "Wire.endTransmission()"? You know that the "endTransmission" is actually the start of transmission.

  Mikael Patel

  – Mikael Patel

  2019-08-09 09:24:24 +00:00

  CommentedAug 9, 2019 at 9:24
• Does the evaluation board run on 3.3V?

  chrisl

  – chrisl

  2019-08-09 09:37:14 +00:00

  CommentedAug 9, 2019 at 9:37
• i didn't had understood that the transmission started only after the endTransmission. I have added the delay() because into the I2C scanner i had to add a delay(100) between the beginTransmission and endTransmission or the scanner was blocking at the address tryed

  Maxence Ginet

  – Maxence Ginet

  2019-08-09 09:55:21 +00:00

  CommentedAug 9, 2019 at 9:55
• @chrisl i tryed with the both alimentation pin of the Uno the 3.3 and the 5V and got the same result

  Maxence Ginet

  – Maxence Ginet

  2019-08-09 10:01:15 +00:00

  CommentedAug 9, 2019 at 10:01
• But the Uno will try to raise SDA and SCL to 5V, while the evaluation board would only raise it to 3.3V. So there will be a cross current. If you want to connect a 5V and a 3.3V device via I2C, you definitely need a level shifter.

  chrisl

  – chrisl

  2019-08-09 10:07:09 +00:00

  CommentedAug 9, 2019 at 10:07

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